The present invention relates to a reciprocating internal combustion engine suitable for automotive vehicles, and particularly to the improvements of an internal combustion engine having reciprocating pistons, each connected to an engine crankshaft via a linkage.
In typical reciprocating internal combustion engines, a crank pin of a crankshaft is connected to a piston pin of a piston usually by means of a single link known as a xe2x80x9cconnecting rodxe2x80x9d. The internal combustion engine having reciprocating pistons each connected to the crankshaft via the single link (connecting rod) will be hereinafter referred to as a xe2x80x9csingle-link type reciprocating piston enginexe2x80x9d. In the single-link type reciprocating engines, the length of the connecting rod is finite, and therefore higher-order vibration (oscillation) components except a first-order vibration component are involved in a vibrating system of reciprocating motion of the piston, synchronizing rotary motion of the crankshaft. In order to vary a compression ratio between the volume in the engine cylinder with the piston at bottom dead center (BDC) and the volume with the piston at top dead center (TDC) depending upon engine operating conditions such as engine speed, in recent years, there have been proposed multiple-link type reciprocating engines. One such multiple-link type reciprocating engine has been disclosed in Japanese Patent Provisional Publication No. 9-228858.
Referring to FIG. 9, there are shown variations in the piston acceleration (indicated by the heavy solid line in FIG. 9) and fluctuations in each of piston accelerations having different orders, that is, the amplitude of each of 1st-order, 2nd-order, 3rd-order, and 4th-order vibration components, in a single-link type reciprocating piston engine. In FIG. 9, the thin solid line indicates the change in the first-order piston acceleration corresponding to the first-order vibration component of the vibrating system of reciprocating motion of the piston, synchronizing rotary motion of the crankshaft. The broken line shown in FIG. 9 indicates the change in the second-order piston acceleration corresponding to the second-order vibration component of the vibrating system of reciprocating motion of the piston. The one-dotted line shown in FIG. 9 indicates the change in the third-order piston acceleration corresponding to the third-order vibration component of the vibrating system of reciprocating motion of the piston, whereas the two-dotted line shown in FIG. 9 indicates the change in the fourth-order piston acceleration corresponding to the fourth-order vibration component of the vibrating system of reciprocating motion of the piston. As can be seen from the graph shown in FIG. 9, in the single-link type reciprocating piston engine, in addition to the first-order piston-acceleration component (see the thin solid line of the characteristic curve shown in FIG. 9), the second-order piston-acceleration component (see the broken line of the characteristic curve shown in FIG. 9) is involved in the vibrating system of reciprocating motion of the piston. As clearly seen from the characteristic curves shown in FIG. 9, the amplitude of the second-order piston-acceleration component is relatively large in comparison with the third-order and fourth-order piston-acceleration components. Actually, the amplitude of the second-order piston-acceleration component is about one third the first-order piston-acceleration component. For the reasons set forth above, in the single-link type reciprocating engine, a vibrating force, occurring mainly owing to the first-order and second-order vibration components, acts on the engine, in particular the engine block. By providing counter weights or balance weights, each located opposite to its adjacent crank pin of the crankshaft, it is possible to effectively reduce or suppress the first-order vibration occurring due to the first-order vibration component of the vibrating system of reciprocating piston, synchronizing rotary motion of the crankshaft. In multiple cylinder engines, by way of contriving of the layout of cylinders, it is possible to satisfactorily suppress the first-order vibration. In comparison with the first-order vibration, it is difficult to sufficiently suppress the second-order vibration occurring due to the second-order vibration component of the vibrating system of reciprocating piston, synchronizing rotary motion of the crankshaft, by way of only the layout of cylinders. Generally, booming noise occurring in the vehicle compartment is caused by such second-order vibrations. The longer the length of the connecting rod, the smaller the amplitudes of the first-order and higher-order vibration components and, hence, the vibrating system of reciprocating motion of the piston can approach to a simple harmonic vibration that vibration at a point in a system is simple harmonic when the displacement with respect to time is described by a simple sine function. On one hand, the longer connecting rod contributes to a reduction in the second-order piston-acceleration component, but, on the other hand, the longer connecting rod increases the overall height of the engine, thereby resulting in an increase in total weight of the engine and preventing easy mounting of the engine on the vehicle engine mount.
Accordingly, it is an object of the invention to provide an improved reciprocating internal combustion engine, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a multiple-link type reciprocating engine, which is capable of effectively reducing a second-order vibration component of a vibrating system of reciprocating motion of each of pistons, synchronizing rotary motion of a crankshaft, without increasing the overall height of the engine, by properly setting dimensions, shapes, layout and relative positions of links via which a crank pin of the crankshaft is connected to a piston pin of each piston.
In order to accomplish the aforementioned and other objects of the present invention, a multiple-link type reciprocating internal combustion engine comprises a piston movable through a stroke in the engine and having a piston pin, a crankshaft changing reciprocating motion of the piston into rotating motion and having a crank pin, a linkage comprising an upper link connected to the piston pin, a lower link connecting the upper link to the crank pin, and a third link pivoted at one end to a body of the engine and connected at its other end to either of the upper and lower links to permit oscillating motion of the third link on the body of the engine, and the upper link, the lower link, and the third link being dimensioned and laid out so that an amplitude of a second-order vibration component of a vibrating system of reciprocating motion of the piston, synchronizing rotary motion of the crankshaft, is reduced to below a predetermined threshold value. It is preferable that the predetermined threshold value of the amplitude of the second-order vibration component is set to be less than or equal to 10% of an amplitude of a first-order vibration component of the vibrating system of reciprocating motion of the piston, synchronizing rotary motion of the crankshaft.
According to another aspect of the invention, a multiple-link type reciprocating internal combustion engine comprises a piston movable through a stroke in the engine and having a piston pin, a crankshaft changing reciprocating motion of the piston into rotating motion and having a crank pin, a linkage comprising an upper link connected to the piston pin, a lower link connecting the upper link to the crank pin, and a third link pivoted at one end to a body of the engine and connected at its other end to either of the upper and lower links to permit oscillating motion of the third link on the body of the engine, and the upper link, the lower link, and the third link being dimensioned and laid out so that an amplitude of a second-order vibration component of a vibrating system of reciprocating motion of the piston, synchronizing rotary motion of the crankshaft, is generally equal to an amplitude of a third-order vibration component of the vibrating system. Preferably, a pivot of oscillating motion of the third link is displaceable with respect to the body of the engine, to vary a compression ratio of the engine. More preferably, the amplitude of the second-order vibration component of the vibrating system of reciprocating motion of the piston, produced when the pivot of the third link is kept at an angular position corresponding to a first compression ratio, is set to be less than the amplitude of the second-order vibration component of the vibrating system of reciprocating motion of the piston, produced when the pivot of the third link is kept at an angular position corresponding to a second compression ratio less than the first compression ratio. It is preferable that a distance from an axis of the crank pin to a trace line of reciprocating motion of an axis of the piston pin is shorter than a distance from a pivot of oscillating motion of the third link to the trace line of reciprocating motion of the axis of the piston pin, at least when the piston is near either of TDC and BDC. When a center of rotation of the crankshaft is defined as an origin O, a directed line Ox parallel to a direction perpendicular to the piston pin and a trace line of reciprocating motion of an axis of the piston pin as viewed from a direction of the axis of the piston pin is taken as an x-axis, a directed line Oy parallel to the trace line of reciprocating motion of the axis of the piston pin is taken as a y-axis, the directed lines Ox and Oy intersecting at a right angle at the origin O, and a direction of rotation of the crankshaft is defined as a counterclockwise direction as viewed from a front end of the engine, preferably, an x-coordinate of a pivot of oscillating motion of the third link is set to a positive value and an x-coordinate of the trace line of reciprocating motion of the axis of the piston pin is set to a negative value. More preferably, the multiple-link type reciprocating internal combustion engine may further comprise a first connecting portion via which the lower link and the third link are connected to each other to permit relative rotation of the lower link about an axis of the first connecting portion and relative rotation of the third link about the axis of the first connecting portion and a second connecting portion via which the upper link and the lower link are connected to each other to permit relative rotation of the upper link about an axis of the second connecting portion and relative rotation of the lower link about the axis of the second connecting portion, and it is preferable that the upper link, the lower link, and the third link are dimensioned and laid out, to satisfy a predetermined ratio                               L1          ⁢                      :                    ⁢          L2          ⁢                      :                    ⁢          L3          ⁢                      :                    ⁢          L4          ⁢                      :                    ⁢          L5          ⁢                      :                    ⁢          L6          ⁢                      :                    ⁢          XC          ⁢                      :                    ⁢          YC          ⁢                      :                    ⁢          x4                ≈                                          1          ⁢                      :                    ⁢          2.4          ⁢                      :                    ⁢          2.65                ∼                  3.5          ⁢                      :                    ⁢          0.69          ⁢                      :                    ⁢          3.0                ∼                  3.4          ⁢                      :                    ⁢          3.3                ∼                  3.55          ⁢                      :                    ⁢          3.2                ∼                              3.55            ⁢                          :                                -          2                ∼                                                                    -              1.35                        ⁢                          :                                -          1                ∼                  -          0.6                    
where L1 is a distance between the center of rotation of the crankshaft and an axis of the crank pin, L2 is a distance between the axis of the crank pin and an axis of the first connecting portion, L3 is a length of the third link, L4 is a distance between the axis of the crank pin and an axis of the second connecting portion, L5 is a distance between the axes of the first and second connecting portions, L6 is a length of the upper link, (XC, YC) are coordinates of the pivot of oscillating motion of the third link, and x4 is the x-coordinate of the trace line of reciprocating motion of the axis of the piston pin.
According to a still further aspect of the invention, a multiple-link type reciprocating internal combustion engine comprises a piston movable through a stroke in the engine and having a piston pin, a crankshaft changing reciprocating motion of the piston into rotating motion and having a crank pin, a linkage comprising an upper link connected to the piston pin, a lower link connecting the upper link to the crank pin, and a third link pivoted at one end to a body of the engine and connected at its other end to either of the upper and lower links to permit oscillating motion of the third link on the body of the engine, and the upper link, the lower link, and the third link being dimensioned and laid out so that an amplitude of a second-order vibration component of a vibrating system of reciprocating motion of the piston, synchronizing rotary motion of the crankshaft, is reduced to below a predetermined threshold value, while realizing the same piston stroke and engine-cylinder height as a single-link type reciprocating internal combustion engine in which a piston pin and a crank pin are connected to each other by a single link.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.